With the recent accelerated reduction in the size and weight of mobile information terminals such as cellphones, laptop computers and smartphones, there is a demand for higher capacities of batteries that power such devices. Nonaqueous electrolyte secondary batteries, which are charged and discharged by the movement of lithium ions between positive and negative electrodes, have a high energy density and a high capacity and are widely used as power supplies for driving the above mobile information terminals.
Further, nonaqueous electrolyte secondary batteries recently attract attention as power supplies for powering electric tools, electric vehicles and the like, and are expected to find a wider range of applications. Such power supplies are required to have a high capacity for long use and also to have high output characteristics.
To attain an enhancement in output characteristics, Patent Literature 1 suggests to use, as a negative electrode active material, a mixture of graphite particles obtained by impregnating and coating natural graphite with a pitch-carbon black mixture followed by calcination, and carbonaceous particles obtained by calcining a pitch-carbon black mixture.
Patent Literature 2 discloses that output characteristics at low temperatures are enhanced by using a negative electrode material which includes a carbon material capable of storing and releasing lithium ions and a compound having a Group 13 element in the periodic table.